Cyanoguanidine derivatives synthesized by known processes are characterized by imino-nitrile guanidine structures having the following formula: ##STR3##
The stable conformations of the cyanoguanidines of formula II are represented by the following structures: ##STR4##
Structures IIa and IIb represent the anti(--NHR.sub.2) and syn(--NHR.sub.2) geometrical isomers of the formula II cyanoguanidines. These isomers do not demonstrate the phenomenon of tautomery and thus, are not intermediates for the production of amino-nitrile and imino-alkyl cyanoguanidines having the following formula: ##STR5## In solution, the IIa and IIb isomers do not transform into each other. A high energy barrier prevents establishment of either a tautomeric or an E to Z isomeric equilibrium. This high energy barrier results from the rapidity of inversion of the --NCN group (probably by a rotational-bond mechanism) which is greater than the rate of rotation of the --NHR.sub.1 and --NHR.sub.2 groups.